|#m1 #Hind >times_pi >Hind %
]
qed.
+
+theorem exp_sigma_l: ∀n,a,p,f.
+ ∏_{i < n | p i} (exp a (f i)) = exp a (∑_{i < n | p i}(f i)).
+#n #a #p #f elim n // #i #Hind cases (true_or_false (p i)) #Hc
+ [>bigop_Strue [>bigop_Strue [>Hind >exp_plus_times // |//] |//]
+ |>bigop_Sfalse [>bigop_Sfalse [@Hind|//] | //]
+ ]
+qed.