1. A computer system for visually representing logical and mathematical expressions comprising: a. means for displaying a display window, the display window comprising: an IF box created by a user for entry of an expression for determining the value of a condition; a DO box for entry of an expression representing a calculation to be performed in response to a first value of the condition determined according to the expression displayed in the IF box; and an OTHERWISE box created automatically in response to creation of the IF box, for entry of an expression representing a calculation to be performed in response to a second value of the condition determined in the IF box; means for recognizing a logical relationship in a calculation of the displayed boxes and interpreting the expressions contained in the boxes; and means for causing the computer system to determine the value of the condition in the IF box and then, in response to its value, for performing either the calculation in the DO box or the calculation in the OTHERWISE box.