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Projective line

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22: 712: 663: 614: 481: 1527:) action on a projective line, replacing "field" by "KT-field" (generalizing the inverse to a weaker kind of involution), and "PGL" by a corresponding generalization of projective linear maps. 1826:
is a rational curve that lies in no proper linear subspace; it is known that there is only one example (up to projective equivalence), given parametrically in homogeneous coordinates as
136:. The statement and the proof of many theorems of geometry are simplified by the resultant elimination of special cases; for example, two distinct projective lines in a 540: 1018: 1110: 369: 1446: 884: 264: 1956: 1262:
points. In all other respects it is no different from projective lines defined over other types of fields. In the terms of homogeneous coordinates ,
669: 620: 563: 1715:. This is the beginning of methods in algebraic geometry that are inductive on dimension. The rational maps play a role analogous to the 405: 2379: 1519:. Indeed, a generalized converse is true: a sharply 3-transitive group action is always (isomorphic to) a generalized form of a PGL 143:
There are many equivalent ways to formally define a projective line; one of the most common is to define a projective line over a
1598: 86: 2471: 2108: 2068: 1949: 58: 1335: 2537: 2159: 2058: 65: 2527: 1922: 105: 1780:
may give an indeterminate result after a rational map.) This gives a picture in which the main geometric feature is
2237: 1942: 39: 1869: 72: 2384: 2305: 2295: 2232: 43: 1982: 1770:) will in fact be everywhere defined. (That is not the case if there are singularities, since for example a 54: 2567: 2202: 2098: 2461: 2425: 2124: 2037: 1864: 1796: 2435: 2073: 1781: 1512: 1331: 2562: 2481: 1186: 1165: 2394: 2374: 2310: 2227: 2129: 2088: 1859: 2285: 2093: 1724: 1387: 1228: 213: 32: 2078: 1807: 1548: 1471: 1168: 504: 2192: 890: 2456: 2154: 2103: 1992: 1912: 1819: 1024: 79: 287: 2532: 2404: 2063: 1716: 1568: 1560: 1395: 1126: 274: 187: 2315: 8: 2369: 2247: 2212: 2169: 2149: 1815: 1788: 1676: 1552: 727: 144: 2499: 2290: 2270: 2083: 1622: 1220: 2242: 223: 2399: 2346: 2217: 2032: 2027: 1918: 1657: 1610: 1347: 1292: 1145: 384: 208: 132: 2389: 2275: 2252: 1874: 1811: 1720: 1224: 1216: 171: 137: 2504: 2320: 2262: 2164: 1966: 1849: 1734:
is now taken to be of dimension 1, we get a picture of a typical algebraic curve
1536: 159: 127: 2187: 2012: 1997: 1974: 1792: 1207: 2556: 2519: 2300: 2280: 2207: 2002: 1934: 1836: 1571:. In general a (non-singular) curve of genus 0 is rationally equivalent over 1198: 1582:, which is itself birationally equivalent to projective line if and only if 717:
Translating this arithmetic in terms of homogeneous coordinates gives, when
2466: 2440: 2430: 2420: 2222: 2042: 1879: 1772: 1680: 1240: 1172: 167: 1695:), that is not constant. The image will omit only finitely many points of 1463:
lying in it, but the symmetries of the projective line can move the point
2341: 2179: 1854: 1516: 1315: 1161: 1132: 178: 119: 2336: 1311: 170:. This definition is a special instance of the general definition of a 707:{\displaystyle x+\infty =\infty \quad {\text{if}}\quad x\not =\infty } 2197: 1503:). This amount of specification 'uses up' the three dimensions of PGL 658:{\displaystyle x\cdot \infty =\infty \quad {\text{if}}\quad x\not =0} 609:{\displaystyle {\frac {1}{0}}=\infty ,\qquad {\frac {1}{\infty }}=0,} 21: 1898: 1594:
can be used as origin to make explicit the birational equivalence.
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Much more is true, in that some transformation can take any given
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says that there exists a homography that will transform any point
476:{\displaystyle \left\{\in \mathbf {P} ^{1}(K)\mid x\in K\right\}.} 2509: 2494: 2489: 1358:) to emphasise the projective nature of these transformations. 1202: 1750:
is non-singular (which is no loss of generality starting with
1451:
express a one-dimensional subspace by a single non-zero point
1192: 1576: 1667:, other than a single point, has a subfield isomorphic with 1799:, the genus then depends only on the type of ramification. 1917:, Graduate Texts in Mathematics, vol. 133, Springer, 1205:. Hence the complex projective line is also known as the 140:
meet in exactly one point (there is no "parallel" case).
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The projective line may be identified with the line
1535:The projective line is a fundamental example of an 46:. Unsourced material may be challenged and removed. 1758:)), it can be shown that such a rational map from 1440: 1104: 1012: 878: 706: 657: 608: 534: 475: 363: 258: 1467:to any other, and it is in no way distinguished. 2554: 1539:. From the point of view of algebraic geometry, 1156:An example is obtained by projecting points in 126:is, roughly speaking, the extension of a usual 1964: 1153:creating a closed loop or topological circle. 1950: 1703:), and the inverse image of a typical point 277:if they differ by an overall nonzero factor 1201:results in a space that is topologically a 1193:Complex projective line: the Riemann sphere 273:that are not both zero. Two such pairs are 1957: 1943: 1515:. The computational aspect of this is the 199:An arbitrary point in the projective line 194: 1795:of the projective line. According to the 1139:. It may also be thought of as the line 106:Learn how and when to remove this message 545:This allows to extend the arithmetic on 1511:); in other words, the group action is 1120: 2555: 2380:Clifford's theorem on special divisors 1910: 1149:∞; the point connects to both ends of 1938: 1530: 1234: 1227:theory, as the simplest example of a 391:may be identified with the subset of 1899:Action of PGL(2) on Projective Space 1601:of the projective line is the field 375:Line extended by a point at infinity 44:adding citations to reliable sources 15: 1563:, it is the unique such curve over 13: 2538:Vector bundles on algebraic curves 2472:Weber's theorem (Algebraic curves) 2069:Hasse's theorem on elliptic curves 2059:Counting points on elliptic curves 1914:Algebraic Geometry: A First Course 1791:, may be presented abstractly, as 1679:, this means that there will be a 1197:Adding a point at infinity to the 701: 685: 679: 636: 630: 592: 580: 508: 494:) except one, which is called the 14: 2579: 1305: 486:This subset covers all points in 158:), as the set of one-dimensional 1840:for the first interesting case. 1350:for the group, often written PGL 1189:, which distinguishes ∞ and −∞. 1175:we can take the quotient by the 434: 217:, which take the form of a pair 20: 2160:Hurwitz's automorphisms theorem 1870:Projectively extended real line 1266:of these points have the form: 694: 688: 645: 639: 586: 31:needs additional citations for 2385:Gonality of an algebraic curve 2296:Differential of the first kind 1904: 1901:– see comment and cited paper. 1892: 1435: 1417: 1411: 1399: 1310:Quite generally, the group of 1096: 1070: 1055: 1028: 1004: 958: 952: 926: 920: 894: 870: 844: 798: 795: 789: 763: 757: 731: 526: 514: 450: 444: 426: 414: 355: 323: 317: 291: 253: 227: 1: 2528:Birkhoff–Grothendieck theorem 2238:Nagata's conjecture on curves 2109:Schoof–Elkies–Atkin algorithm 1983:Five points determine a conic 1885: 1675:). From the point of view of 1590:; geometrically such a point 1131:The projective line over the 177:The projective line over the 2099:Supersingular elliptic curve 1723:, and indeed in the case of 1637:are precisely the group PGL 1617:, in a single indeterminate 1322:acts on the projective line 1215:). It is in constant use in 7: 2306:Riemann's existence theorem 2233:Hilbert's sixteenth problem 2125:Elliptic curve cryptography 2038:Fundamental pair of periods 1865:Projective line over a ring 1843: 1727:the two concepts coincide. 1239:The projective line over a 1143:together with an idealised 1115: 387:. More precisely, the line 207:) may be represented by an 10: 2584: 2436:Moduli of algebraic curves 1810:to a projective line (see 1386:of choice of coordinates: 1124: 2518: 2480: 2449: 2413: 2362: 2355: 2329: 2261: 2178: 2142: 2117: 2051: 2020: 2011: 1973: 1787:Many curves, for example 1586:has a point defined over 1187:extended real number line 535:{\displaystyle \infty =.} 2203:Cayley–Bacharach theorem 2130:Elliptic curve primality 1725:compact Riemann surfaces 1465:∞ = [1 : 0] 1013:{\displaystyle \cdot =,} 2462:Riemann–Hurwitz formula 2426:Gromov–Witten invariant 2286:Compact Riemann surface 2074:Mazur's torsion theorem 1808:birationally equivalent 1797:Riemann–Hurwitz formula 1388:homogeneous coordinates 1229:compact Riemann surface 1105:{\displaystyle ^{-1}=.} 214:homogeneous coordinates 195:Homogeneous coordinates 2079:Modular elliptic curve 1442: 1298:may be represented as 1169:diametrically opposite 1106: 1014: 880: 708: 659: 610: 536: 477: 365: 364:{\displaystyle \sim .} 260: 1993:Rational normal curve 1860:Möbius transformation 1820:rational normal curve 1717:meromorphic functions 1707:will be of dimension 1490:to any other 3-tuple 1443: 1441:{\displaystyle \sim } 1107: 1015: 881: 709: 660: 611: 537: 478: 366: 261: 162:of a two-dimensional 2533:Stable vector bundle 2405:Weil reciprocity law 2395:Riemann–Roch theorem 2375:Brill–Noether theory 2311:Riemann–Roch theorem 2228:Genus–degree formula 2089:Mordell–Weil theorem 2064:Division polynomials 1911:Harris, Joe (1992), 1822:in projective space 1789:hyperelliptic curves 1569:rational equivalence 1561:algebraically closed 1513:sharply 3-transitive 1499:of distinct points ( 1396: 1300:[1 : 0] 1171:points. In terms of 1137:real projective line 1127:Real projective line 1121:Real projective line 1025: 891: 728: 719:[0 : 0] 670: 621: 564: 505: 406: 288: 224: 188:Real projective line 130:by a point called a 40:improve this article 2568:Projective geometry 2356:Structure of curves 2248:Quartic plane curve 2170:Hyperelliptic curve 2150:De Franchis theorem 2094:Nagell–Lutz theorem 1806:is a curve that is 1677:birational geometry 1648:Any function field 1645:) discussed above. 1623:field automorphisms 1501:triple transitivity 1366:to any other point 879:{\displaystyle +=,} 150:, commonly denoted 2363:Divisors on curves 2155:Faltings's theorem 2104:Schoof's algorithm 2084:Modularity theorem 1611:rational functions 1531:As algebraic curve 1438: 1382:) is therefore an 1291:and the remaining 1235:For a finite field 1221:algebraic geometry 1211:(or sometimes the 1102: 1010: 876: 704: 655: 606: 557:) by the formulas 532: 473: 361: 256: 2550: 2549: 2546: 2545: 2457:Hasse–Witt matrix 2400:Weierstrass point 2347:Smooth completion 2316:TeichmĂŒller space 2218:Cubic plane curve 2138: 2137: 2052:Arithmetic theory 2033:Elliptic integral 2028:Elliptic function 1738:presented 'over' 1658:algebraic variety 1372:point at infinity 1348:homogeneous space 1146:point at infinity 692: 643: 595: 575: 496:point at infinity 385:point at infinity 209:equivalence class 133:point at infinity 116: 115: 108: 90: 55:"Projective line" 2575: 2563:Algebraic curves 2390:Jacobian variety 2360: 2359: 2263:Riemann surfaces 2253:Real plane curve 2213:Cramer's paradox 2193:BĂ©zout's theorem 2018: 2017: 1967:algebraic curves 1959: 1952: 1945: 1936: 1935: 1929: 1927: 1908: 1902: 1896: 1875:Projective range 1812:rational variety 1721:complex analysis 1714: 1489: 1466: 1462: 1447: 1445: 1444: 1439: 1301: 1286: 1275: 1261: 1225:complex manifold 1217:complex analysis 1181: 1111: 1109: 1108: 1103: 1095: 1094: 1082: 1081: 1066: 1065: 1053: 1052: 1040: 1039: 1019: 1017: 1016: 1011: 1003: 1002: 993: 992: 980: 979: 970: 969: 951: 950: 938: 937: 919: 918: 906: 905: 885: 883: 882: 877: 869: 868: 859: 858: 843: 842: 833: 832: 820: 819: 810: 809: 788: 787: 775: 774: 756: 755: 743: 742: 721:does not occur: 720: 713: 711: 710: 705: 693: 690: 664: 662: 661: 656: 644: 641: 615: 613: 612: 607: 596: 588: 576: 568: 541: 539: 538: 533: 482: 480: 479: 474: 469: 465: 443: 442: 437: 370: 368: 367: 362: 354: 353: 338: 337: 316: 315: 303: 302: 265: 263: 262: 259:{\displaystyle } 257: 252: 251: 239: 238: 172:projective space 138:projective plane 111: 104: 100: 97: 91: 89: 48: 24: 16: 2583: 2582: 2578: 2577: 2576: 2574: 2573: 2572: 2553: 2552: 2551: 2542: 2514: 2505:Delta invariant 2476: 2445: 2409: 2370:Abel–Jacobi map 2351: 2325: 2321:Torelli theorem 2291:Dessin d'enfant 2271:Belyi's theorem 2257: 2243:PlĂŒcker formula 2174: 2165:Hurwitz surface 2134: 2113: 2047: 2021:Analytic theory 2013:Elliptic curves 2007: 1988:Projective line 1975:Rational curves 1969: 1963: 1933: 1932: 1925: 1909: 1905: 1897: 1893: 1888: 1850:Algebraic curve 1846: 1793:ramified covers 1708: 1640: 1537:algebraic curve 1533: 1522: 1506: 1498: 1484: 1482: 1464: 1452: 1397: 1394: 1393: 1353: 1308: 1299: 1285: 1277: 1271: 1256: 1250: 1237: 1195: 1179: 1129: 1123: 1118: 1090: 1086: 1077: 1073: 1058: 1054: 1048: 1044: 1035: 1031: 1026: 1023: 1022: 998: 994: 988: 984: 975: 971: 965: 961: 946: 942: 933: 929: 914: 910: 901: 897: 892: 889: 888: 864: 860: 854: 850: 838: 834: 828: 824: 815: 811: 805: 801: 783: 779: 770: 766: 751: 747: 738: 734: 729: 726: 725: 718: 689: 671: 668: 667: 640: 622: 619: 618: 587: 567: 565: 562: 561: 506: 503: 502: 438: 433: 432: 413: 409: 407: 404: 403: 377: 349: 345: 333: 329: 311: 307: 298: 294: 289: 286: 285: 269:of elements of 247: 243: 234: 230: 225: 222: 221: 197: 124:projective line 112: 101: 95: 92: 49: 47: 37: 25: 12: 11: 5: 2581: 2571: 2570: 2565: 2548: 2547: 2544: 2543: 2541: 2540: 2535: 2530: 2524: 2522: 2520:Vector bundles 2516: 2515: 2513: 2512: 2507: 2502: 2497: 2492: 2486: 2484: 2478: 2477: 2475: 2474: 2469: 2464: 2459: 2453: 2451: 2447: 2446: 2444: 2443: 2438: 2433: 2428: 2423: 2417: 2415: 2411: 2410: 2408: 2407: 2402: 2397: 2392: 2387: 2382: 2377: 2372: 2366: 2364: 2357: 2353: 2352: 2350: 2349: 2344: 2339: 2333: 2331: 2327: 2326: 2324: 2323: 2318: 2313: 2308: 2303: 2298: 2293: 2288: 2283: 2278: 2273: 2267: 2265: 2259: 2258: 2256: 2255: 2250: 2245: 2240: 2235: 2230: 2225: 2220: 2215: 2210: 2205: 2200: 2195: 2190: 2184: 2182: 2176: 2175: 2173: 2172: 2167: 2162: 2157: 2152: 2146: 2144: 2140: 2139: 2136: 2135: 2133: 2132: 2127: 2121: 2119: 2115: 2114: 2112: 2111: 2106: 2101: 2096: 2091: 2086: 2081: 2076: 2071: 2066: 2061: 2055: 2053: 2049: 2048: 2046: 2045: 2040: 2035: 2030: 2024: 2022: 2015: 2009: 2008: 2006: 2005: 2000: 1998:Riemann sphere 1995: 1990: 1985: 1979: 1977: 1971: 1970: 1962: 1961: 1954: 1947: 1939: 1931: 1930: 1923: 1903: 1890: 1889: 1887: 1884: 1883: 1882: 1877: 1872: 1867: 1862: 1857: 1852: 1845: 1842: 1832: 1831: 1804:rational curve 1778:crosses itself 1776:where a curve 1638: 1599:function field 1532: 1529: 1520: 1504: 1494: 1478: 1449: 1448: 1437: 1434: 1431: 1428: 1425: 1422: 1419: 1416: 1413: 1410: 1407: 1404: 1401: 1351: 1307: 1306:Symmetry group 1304: 1289: 1288: 1281: 1246: 1236: 1233: 1208:Riemann sphere 1194: 1191: 1135:is called the 1125:Main article: 1122: 1119: 1117: 1114: 1113: 1112: 1101: 1098: 1093: 1089: 1085: 1080: 1076: 1072: 1069: 1064: 1061: 1057: 1051: 1047: 1043: 1038: 1034: 1030: 1020: 1009: 1006: 1001: 997: 991: 987: 983: 978: 974: 968: 964: 960: 957: 954: 949: 945: 941: 936: 932: 928: 925: 922: 917: 913: 909: 904: 900: 896: 886: 875: 872: 867: 863: 857: 853: 849: 846: 841: 837: 831: 827: 823: 818: 814: 808: 804: 800: 797: 794: 791: 786: 782: 778: 773: 769: 765: 762: 759: 754: 750: 746: 741: 737: 733: 715: 714: 703: 700: 697: 687: 684: 681: 678: 675: 665: 654: 651: 648: 638: 635: 632: 629: 626: 616: 605: 602: 599: 594: 591: 585: 582: 579: 574: 571: 543: 542: 531: 528: 525: 522: 519: 516: 513: 510: 484: 483: 472: 468: 464: 461: 458: 455: 452: 449: 446: 441: 436: 431: 428: 425: 422: 419: 416: 412: 383:extended by a 376: 373: 372: 371: 360: 357: 352: 348: 344: 341: 336: 332: 328: 325: 322: 319: 314: 310: 306: 301: 297: 293: 267: 266: 255: 250: 246: 242: 237: 233: 229: 196: 193: 114: 113: 28: 26: 19: 9: 6: 4: 3: 2: 2580: 2569: 2566: 2564: 2561: 2560: 2558: 2539: 2536: 2534: 2531: 2529: 2526: 2525: 2523: 2521: 2517: 2511: 2508: 2506: 2503: 2501: 2498: 2496: 2493: 2491: 2488: 2487: 2485: 2483: 2482:Singularities 2479: 2473: 2470: 2468: 2465: 2463: 2460: 2458: 2455: 2454: 2452: 2448: 2442: 2439: 2437: 2434: 2432: 2429: 2427: 2424: 2422: 2419: 2418: 2416: 2412: 2406: 2403: 2401: 2398: 2396: 2393: 2391: 2388: 2386: 2383: 2381: 2378: 2376: 2373: 2371: 2368: 2367: 2365: 2361: 2358: 2354: 2348: 2345: 2343: 2340: 2338: 2335: 2334: 2332: 2330:Constructions 2328: 2322: 2319: 2317: 2314: 2312: 2309: 2307: 2304: 2302: 2301:Klein quartic 2299: 2297: 2294: 2292: 2289: 2287: 2284: 2282: 2281:Bolza surface 2279: 2277: 2276:Bring's curve 2274: 2272: 2269: 2268: 2266: 2264: 2260: 2254: 2251: 2249: 2246: 2244: 2241: 2239: 2236: 2234: 2231: 2229: 2226: 2224: 2221: 2219: 2216: 2214: 2211: 2209: 2208:Conic section 2206: 2204: 2201: 2199: 2196: 2194: 2191: 2189: 2188:AF+BG theorem 2186: 2185: 2183: 2181: 2177: 2171: 2168: 2166: 2163: 2161: 2158: 2156: 2153: 2151: 2148: 2147: 2145: 2141: 2131: 2128: 2126: 2123: 2122: 2120: 2116: 2110: 2107: 2105: 2102: 2100: 2097: 2095: 2092: 2090: 2087: 2085: 2082: 2080: 2077: 2075: 2072: 2070: 2067: 2065: 2062: 2060: 2057: 2056: 2054: 2050: 2044: 2041: 2039: 2036: 2034: 2031: 2029: 2026: 2025: 2023: 2019: 2016: 2014: 2010: 2004: 2003:Twisted cubic 2001: 1999: 1996: 1994: 1991: 1989: 1986: 1984: 1981: 1980: 1978: 1976: 1972: 1968: 1960: 1955: 1953: 1948: 1946: 1941: 1940: 1937: 1926: 1924:9780387977164 1920: 1916: 1915: 1907: 1900: 1895: 1891: 1881: 1878: 1876: 1873: 1871: 1868: 1866: 1863: 1861: 1858: 1856: 1853: 1851: 1848: 1847: 1841: 1839: 1838: 1837:Twisted cubic 1829: 1828: 1827: 1825: 1821: 1817: 1813: 1809: 1805: 1800: 1798: 1794: 1790: 1785: 1783: 1779: 1775: 1774: 1769: 1765: 1761: 1757: 1753: 1749: 1745: 1741: 1737: 1733: 1728: 1726: 1722: 1718: 1712: 1706: 1702: 1698: 1694: 1690: 1686: 1682: 1678: 1674: 1670: 1666: 1662: 1659: 1655: 1651: 1646: 1644: 1636: 1632: 1628: 1624: 1620: 1616: 1612: 1608: 1604: 1600: 1595: 1593: 1589: 1585: 1581: 1578: 1574: 1570: 1566: 1562: 1558: 1554: 1550: 1546: 1542: 1538: 1528: 1526: 1518: 1514: 1510: 1502: 1497: 1493: 1487: 1481: 1477: 1473: 1468: 1460: 1456: 1432: 1429: 1426: 1423: 1420: 1414: 1408: 1405: 1402: 1392: 1391: 1390: 1389: 1385: 1381: 1377: 1373: 1369: 1365: 1361: 1357: 1349: 1345: 1341: 1337: 1333: 1329: 1325: 1321: 1317: 1313: 1303: 1297: 1296: 1284: 1280: 1274: 1269: 1268: 1267: 1265: 1259: 1255:elements has 1254: 1249: 1245: 1242: 1232: 1230: 1226: 1222: 1218: 1214: 1210: 1209: 1204: 1200: 1199:complex plane 1190: 1188: 1183: 1178: 1174: 1170: 1167: 1163: 1159: 1154: 1152: 1148: 1147: 1142: 1138: 1134: 1128: 1099: 1091: 1087: 1083: 1078: 1074: 1067: 1062: 1059: 1049: 1045: 1041: 1036: 1032: 1021: 1007: 999: 995: 989: 985: 981: 976: 972: 966: 962: 955: 947: 943: 939: 934: 930: 923: 915: 911: 907: 902: 898: 887: 873: 865: 861: 855: 851: 847: 839: 835: 829: 825: 821: 816: 812: 806: 802: 792: 784: 780: 776: 771: 767: 760: 752: 748: 744: 739: 735: 724: 723: 722: 698: 695: 682: 676: 673: 666: 652: 649: 646: 633: 627: 624: 617: 603: 600: 597: 589: 583: 577: 572: 569: 560: 559: 558: 556: 552: 548: 529: 523: 520: 517: 511: 501: 500: 499: 497: 493: 489: 470: 466: 462: 459: 456: 453: 447: 439: 429: 423: 420: 417: 410: 402: 401: 400: 398: 394: 390: 386: 382: 358: 350: 346: 342: 339: 334: 330: 326: 320: 312: 308: 304: 299: 295: 284: 283: 282: 280: 276: 272: 248: 244: 240: 235: 231: 220: 219: 218: 216: 215: 210: 206: 202: 192: 191:for details. 190: 189: 184: 180: 175: 173: 169: 165: 161: 157: 153: 149: 146: 141: 139: 135: 134: 129: 125: 121: 110: 107: 99: 96:December 2009 88: 85: 81: 78: 74: 71: 67: 64: 60: 57: â€“  56: 52: 51:Find sources: 45: 41: 35: 34: 29:This article 27: 23: 18: 17: 2467:Prym variety 2441:Stable curve 2431:Hodge bundle 2421:ELSV formula 2223:Fermat curve 2180:Plane curves 2143:Higher genus 2118:Applications 2043:Modular form 1987: 1913: 1906: 1894: 1880:Wheel theory 1835: 1833: 1823: 1803: 1801: 1786: 1782:ramification 1777: 1773:double point 1771: 1767: 1763: 1759: 1755: 1751: 1747: 1746:). Assuming 1743: 1739: 1735: 1731: 1729: 1710: 1704: 1700: 1696: 1692: 1688: 1684: 1681:rational map 1672: 1668: 1664: 1660: 1653: 1649: 1647: 1642: 1634: 1630: 1626: 1618: 1614: 1606: 1602: 1596: 1591: 1587: 1583: 1579: 1572: 1564: 1556: 1549:non-singular 1544: 1540: 1534: 1524: 1508: 1500: 1495: 1491: 1485: 1479: 1475: 1469: 1458: 1454: 1450: 1383: 1379: 1375: 1371: 1367: 1363: 1360:Transitivity 1359: 1355: 1343: 1339: 1332:group action 1327: 1323: 1319: 1316:coefficients 1312:homographies 1309: 1294: 1290: 1282: 1278: 1272: 1263: 1257: 1252: 1247: 1243: 1241:finite field 1238: 1213:Gauss sphere 1212: 1206: 1196: 1185:Compare the 1184: 1173:group theory 1157: 1155: 1150: 1144: 1140: 1136: 1133:real numbers 1130: 716: 554: 550: 546: 544: 495: 491: 487: 485: 396: 392: 388: 380: 378: 278: 270: 268: 212: 204: 200: 198: 186: 176: 168:vector space 163: 155: 151: 147: 142: 131: 123: 117: 102: 93: 83: 76: 69: 62: 50: 38:Please help 33:verification 30: 2342:Polar curve 1855:Cross-ratio 1517:cross-ratio 1295:at infinity 1166:identifying 1162:unit circle 399:) given by 120:mathematics 2557:Categories 2337:Dual curve 1965:Topics in 1886:References 1338:, so that 1336:transitive 275:equivalent 66:newspapers 2450:Morphisms 2198:Bitangent 1551:curve of 1488:= 1, 2, 3 1430:λ 1421:λ 1415:∼ 1270:for each 1164:and then 1160:onto the 1060:− 924:⋅ 702:∞ 686:∞ 680:∞ 637:∞ 631:∞ 628:⋅ 593:∞ 581:∞ 509:∞ 460:∈ 454:∣ 430:∈ 343:λ 327:λ 321:∼ 160:subspaces 1844:See also 1818:is 0. A 1656:) of an 1567:, up to 1472:distinct 1384:artifact 1330:). This 1177:subgroup 1116:Examples 699:≠ 650:≠ 183:manifold 2510:Tacnode 2495:Crunode 1814:); its 1633:) over 1547:) is a 1474:points 1346:) is a 1180:{1, −1} 80:scholar 2490:Acnode 2414:Moduli 1921:  1621:. The 1555:0. If 1370:. The 1293:point 1203:sphere 185:; see 82:  75:  68:  61:  53:  1816:genus 1683:from 1663:over 1613:over 1609:) of 1577:conic 1575:to a 1553:genus 1314:with 181:is a 179:reals 145:field 87:JSTOR 73:books 2500:Cusp 1919:ISBN 1834:See 1709:dim 1597:The 1483:for 1223:and 128:line 122:, a 59:news 1762:to 1730:If 1719:of 1713:− 1 1687:to 1625:of 1559:is 1374:on 1334:is 1318:in 1276:in 1260:+ 1 1251:of 549:to 211:of 118:In 42:by 2559:: 1802:A 1784:. 1457:, 1302:. 1231:. 1219:, 1182:. 691:if 642:if 498:: 281:: 174:. 1958:e 1951:t 1944:v 1928:. 1830:. 1824:P 1768:K 1766:( 1764:P 1760:C 1756:C 1754:( 1752:K 1748:C 1744:K 1742:( 1740:P 1736:C 1732:V 1711:V 1705:P 1701:K 1699:( 1697:P 1693:K 1691:( 1689:P 1685:V 1673:T 1671:( 1669:K 1665:K 1661:V 1654:V 1652:( 1650:K 1643:K 1641:( 1639:2 1635:K 1631:T 1629:( 1627:K 1619:T 1615:K 1607:T 1605:( 1603:K 1592:P 1588:K 1584:C 1580:C 1573:K 1565:K 1557:K 1545:K 1543:( 1541:P 1525:K 1523:( 1521:2 1509:K 1507:( 1505:2 1496:i 1492:R 1486:i 1480:i 1476:Q 1461:) 1459:Y 1455:X 1453:( 1436:] 1433:Y 1427:: 1424:X 1418:[ 1412:] 1409:Y 1406:: 1403:X 1400:[ 1380:K 1378:( 1376:P 1368:R 1364:Q 1356:K 1354:( 1352:2 1344:K 1342:( 1340:P 1328:K 1326:( 1324:P 1320:K 1287:, 1283:q 1279:F 1273:a 1264:q 1258:q 1253:q 1248:q 1244:F 1158:R 1151:K 1141:K 1100:. 1097:] 1092:1 1088:x 1084:: 1079:2 1075:x 1071:[ 1068:= 1063:1 1056:] 1050:2 1046:x 1042:: 1037:1 1033:x 1029:[ 1008:, 1005:] 1000:2 996:y 990:2 986:x 982:: 977:1 973:y 967:1 963:x 959:[ 956:= 953:] 948:2 944:y 940:: 935:1 931:y 927:[ 921:] 916:2 912:x 908:: 903:1 899:x 895:[ 874:, 871:] 866:2 862:y 856:2 852:x 848:: 845:) 840:2 836:x 830:1 826:y 822:+ 817:2 813:y 807:1 803:x 799:( 796:[ 793:= 790:] 785:2 781:y 777:: 772:1 768:y 764:[ 761:+ 758:] 753:2 749:x 745:: 740:1 736:x 732:[ 696:x 683:= 677:+ 674:x 653:0 647:x 634:= 625:x 604:, 601:0 598:= 590:1 584:, 578:= 573:0 570:1 555:K 553:( 551:P 547:K 530:. 527:] 524:0 521:: 518:1 515:[ 512:= 492:K 490:( 488:P 471:. 467:} 463:K 457:x 451:) 448:K 445:( 440:1 435:P 427:] 424:1 421:: 418:x 415:[ 411:{ 397:K 395:( 393:P 389:K 381:K 359:. 356:] 351:2 347:x 340:: 335:1 331:x 324:[ 318:] 313:2 309:x 305:: 300:1 296:x 292:[ 279:λ 271:K 254:] 249:2 245:x 241:: 236:1 232:x 228:[ 205:K 203:( 201:P 166:- 164:K 156:K 154:( 152:P 148:K 109:) 103:( 98:) 94:( 84:· 77:· 70:· 63:· 36:.

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