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### Multiplying elements of D4

I have the following group presentation $D_4 = \langle r,s | r^4 = s^2 = rsrs = 1 \rangle$.

This is written in sage as

F.<r,s> = FreeGroup()
D4 = F / [r^4, s^2, r*s*r*s, 1]
r,s = D4.gens()


Say I wanted to compute s^2, this should equal 1 but sage gives me just s^2.

s^2


output:

s^2


I am doing more involved calculations and I want to return the result in the simplified form. How do I simplify the expression in sage?