i think i got it

A bounded from the bottom

x is a low bound of A

i need to prove that x=inf A

this expression is just the definition of inf

x<=y<=x+e

so i tried to solve it as if i got a formula

I presume that "x" is not inf

then our inf is x+e

now i proove that x+e is not infA

x+e>y

but here i got stuck because in this step i would do a formula operation.

??