64. A computer-readable medium containing instructions for causing a computer system to navigate through a representation of a computational construct, by: receiving input from a user; when the received input is a specification of another computational construct, replacing the computational construct and any of its operands by the other computational construct; and when the received input is a first indicator, navigating a representation of a left operand of the computational construct.
64. A computer-readable medium containing instructions for causing a computer system to navigate through a representation of a computational construct, by: receiving input from a user; when the received input is a specification of another computational construct, replacing the computational construct and any of its operands by the other computational construct; and when the received input is a first indicator, navigating a representation of a left operand of the computational construct. 65. The computer-readable medium of claim 64, further including: when the received input is a second indicator, setting a current selection to a selection of the computational construct representing the binary operator in a left selection mode so that when the user inputs a specification of a binary operator the computational construct will be a right operand of the binary operator.