Cuspidal modular symbols are transportable
William A. Stein and Helena A. Verrill
Abstract: Modular symbols of weight 2 for a congruence subgroup
Γ satisfy the identity
{α, γ(α)} = {β,γ(β)}
for all α,β in the extended
upper half plane, and γ in Γ.
The analogue of this identity is false for
modular symbols of weight greater than 2.
This paper provides a definition of transportable modular symbols,
which are symbols for which an analogue of
the above identity holds, and
proves that every cuspidal symbol can be written
as a transportable symbol.
As a corollary, an algorithm is obtained for computing
periods of cuspforms.
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