⊦ #(s0 ∪ s1) ≤ # s0 + # s1
m + n < #(s0 ∪ s1), # s1 ≤ n, # s0 ≤ m, #(s0 ∪ s1) ≤ # s0 + # s1 ⊦
Used terms: s0, s1