# How to write logical symbols in email or on BlackBoard

Invariably, when you write email with questions regarding logic problems, or when you post on the discussion board on Blackboard, you’ll want to use some of the logical symbols. In email, you will probably be best off using some plain-text approximation of these symbols. In BlackBoard, you can use “HTML4 character entity references” which will be displayed as the actuall symbols by any HTML4 compliant browser (that includes most recent versions of Internet Explorer, Netscape, Mozilla, Opera, Safari, etc.). Here’s a table of suggested plain-text approximations of symbols and HTML4 entity references.

Symbol name   Symbol   Plain Text   HTML4 code
and     ^ or &   &and;
or     v or |   &or;
not   ¬   ~   &not;
conditional     ->   &rarr;
biconditional     <->   &harr;
for all     @ or A   &forall;
there exists     / or E or 3   &exist;
equal   =   =   =
non equal     # or =/=   &ne;
less than or equal     <=   &le;
greater than or equal     >=   &ge;
element of     in   &isin;
not element of     not in   &notin;
subset of     <=   &sube;
union     u   &cup;
intersection     ^   &cap;
powerset     Pow   &weierp;
infinity     infinity   &infin;

To get Greek letters, just put the name of the greek letter between ‘&’ and ‘;’. For instance, ‘&Gamma;’ produces ‘?’, and ‘&alpha;’ produces ‘?’. In email, just write out the name of the letter.

To get subscripts and superscripts on BlackBoard, surround them by <sub>..</sub> or <sup>…</sup>. For instance, ‘x<sub>3</sub>’ produces ‘x2‘ and ‘2<sup>n</sup>’ produces ‘2n‘. In email, use underscore (_) and caret to indicate subscripts and superscripts (e.g., ‘x_3’ and ‘2^n’).