A mathematician, as everyone knows, never makes a mistake … as long as they stay strictly within the theory under study and follow its rules.
In schematic terms, every mathematical argument can be reduced to a simple syllogism involving two statements: the hypothesis H, comprising the information assumed known, and the conclusion T to be proved. If both the hypothesis H and the implication from the hypothesis to the conclusion (denoted HTH\Rightarrow T) are assumed true, then the conclusion T is true.

"Dis tonton, pourquoi tu tousses ?" (Say, Uncle, why are you coughing?), by Fernand Raynaud

From "certain" to "plausible"