Several criticisms can be made of the above "proof", for example by Gull (1989):

A direct construction, in analogy with the above proof for the integer number case, can be performed as follows.

The answer may well be all of the above - a mix of factors not subject to proof, only informed speculation.

The above proof begins by saying that either everyone is drinking, or someone is not drinking.

Since the above proof is constructive, one may extract an algorithm for computing interpolants.

This proof follows the same lines as the above proof.

There are two steps in the above proof that we need to justify:

This can be readily deduced from the above proof.

The above proof applies to all sequential programs, even those with choice points such as guarded commands.

The above proof suggests another interpretation of the Cauchy-Riemann equations.