theorem Th1:
for
i,
k,
m,
n being
Nat st
m + k <= i &
i <= n + k holds
ex
mn being
Nat st
(
mn + k = i &
m <= mn &
mn <= n )
theorem Th2:
for
i,
k,
l,
m,
n being
Nat st
m <= n &
k <= l &
m + k <= i &
i <= n + l holds
ex
mn,
kl being
Nat st
(
mn + kl = i &
m <= mn &
mn <= n &
k <= kl &
kl <= l )
theorem Th3:
for
m,
n being
Nat st
m < n holds
ex
k being
Nat st
(
m + k = n &
k > 0 )