Algebraic modular forms Definition An algebraic modular form of weight k for X(N) over R is a rule f assigning a value to triples (E/R, α, ω), such that f (E, α, uω) = u−k f (E, α, ω) for all u ∈ R× . Short Weierstrass (E) : y2 = x3 + Ax + B ω = dx/2y. Isomorphic to (E0 ) : y2 = x3 + A0 x + B0 by (x, y) 7→ (u2 x, u3 y), A0 = u4 A, B0 = u6 B, ω0 = u−1 ω. Nicolas Mascot p-adic computation of Galois representations