If $4=5$, then $6=8\,$ (yes or no?) I had an argument with a friend about the statement in the title. I asserted that if $4=5$, then $6=8$, as you can derive any conclusion from a false statement. However, he does not agree, and claims that you cannot know that $6$ would equal $8$ if $4$ were to equal $5$. Is the statement in the title correct?

Here is an argument that doesn't involve subtleties of logic:


*

*$4=5$

*$4-3=5-3$

*$1=2$

*$2\times 1=2\times 2$

*$2=4$

*$2+4=4+4$

*$6=8$
