Have a look to the LATEX tutorial in the LATEX forum
Let P(n) be
Check that P(1) is true
Suppose that P(k) is true and show that P(k+1) is true
Let be the propositional function:
(as in my previous posting)
is , which is true. Hence .
PS If you want to see the LaTeX that's been used to generate any of the expressions, just click on them and a little window will open showing you the code.