We show a similar result concerning operations
we call bit cancellation and bit insertion:
Given a function f in GapP and
a polynomial-time computable function k.
Then we ask whether the function f^*(x)
that is obtained from f(x)
by canceling the k(x)th bit in the binary representation of f(x),
or whether the function f^+(x)
that is obtained from f(x)
by inserting a bit at position k(x) in the binary representation of f(x),
is also in GapP.
We give necessary conditions and a sufficient conditions
for GapP being closed under bit cancellation and bit insertion, respectively.