\begin{definition}[Definition:Conditional/Notational Variants/Sign of Illation]
The '''sign of illation''' $-\!\!\!<$ is a notation invented by {{AuthorRef|Charles Sanders Peirce}} to denote the conditional operator.
{{AuthorRef|Charles Sanders Peirce|Peirce}} derives $-\!\!\!<$ as a variant of the sign $\le$ for ''less than or equal to'', so as to denote that:
: $A \mathop {-\!\!\!<} B$
represents the situation such that whenever a particular statement $A$ is true, then so is statement $B$.
It is rarely (if ever) seen nowadays except as a historical curiosity.
\end{definition}