\\e0 is E:y^2=x^3+1 in char zero { e0=ellinit([0,0,0,0,1]) } \\ p is the generic point on e0 { p=[t,Mod(x,x^2-t^3-1)] } \\ f is f_5 whose roots are the x-coords of 5-torsion pts. \\ The "simplify" defies explanation goes around some bug in pari { f=factor(denominator(simplify(ellpow(e0,p,5)[1])))[1,1] } \\a is a root of f in F_{7^12} { a=Mod(Mod(1, 7)*t,Mod(1, 7)*f) } \\v is a square root of a^3+1 in F_{7^24} { v=Mod(Mod(1, 7)*x, Mod(1, 7)*x^2 + Mod(Mod(6, 7)*t^3 + Mod(6, 7), Mod(1, 7)*t^12 + Mod(6, 7)*t^9 + Mod(1, 7)*t^6 + Mod(2, 7)*t^3 + Mod(2, 7))) } \\ q is a 5-torsion point in E mod 7 { q=[a,v] } \\E in char 7 { e=ellinit(Mod(1,7)*[0,0,0,0,1]) } \\ Frobenius of q { qq=[a^7,v^7] } \\ Frobenius of qq { qqq=[a^49,v^49] } \\ qqq + 2q in E mod 7 { rhs=elladd(e,qqq,ellpow(e,q,2)) } \\ finds m for which rhs = m*qq on E { for(m=1,4,if(rhs-ellpow(e,qq,m)==[0,0],print(m" is t modulo 5"))) }