For proving we prove, for arbitrary but fixed values,
.
We prove by the deduction rule.
We assume
and show
.
From and
we obtain by modus ponens
.
By we can take appropriate values such that
.
From and
we obtain by modus ponens
.
From and
we obtain by modus ponens
.
By we can take appropriate values such that
.
By we can take appropriate values such that
.
We prove first
.
For proving we prove, for arbitrary but fixed values,
Formula is proved because
is an instance of it.