Prove

xy(Indiff(x,y)Indiff(y,x))

From:

xy(WeakPref(x,y)WeakPref(y,x))

xyz((WeakPref(x,y)WeakPref(y,z))WeakPref(x,z))

xy(StrongPref(x,y) WeakPref(y,x))

xy(Indiff(x,y)(WeakPref(y,x)WeakPref(x,y)))

Note that all premises don't need to be used.

Thanks!