sigmaEq2 : {A : Type} -> 
           {P : A -> Type} -> 
           {s1: Sigma A P} -> 
           {s2: Sigma A P} ->
           getWitness s1 = getWitness s2 ->
           getProof s1 = getProof s2 ->
           s1 = s2
sigmaEq2 {A} {P} {s1 = (x ** prf)} {s2 = (x ** prf)} Refl Refl = Refl