true ......................................... 71,72\ two-dimensional array ............................ 68\ TZX files ....................................... 156 **U**\ UART ............................................ 155\ UDG ......................................... 49,75,128\ ULA ............................................. 103\ unary ! .......................................... 48\ unary not ........................................ 46\ Unary/Bitwise NOT (!) ............................ 38\ unified sprite ............................... 137,138\ Unsigned .................................... 45,46,47,48\ unsigned expression .............................. 48\ user-defined graphic ............................. 76\ user-defined graphics ............................ 75\ Using Expressions for INPUT ...................... 91\ USR ......................................... 59,75,76 VAL ..................................... 51,52,55,124\ VAL$ ......................................... 51,55\ Variable names ................................... 39\ Variable not found ............................... 92\ vertical size .................................... 96\ visibility ...................................... 136\ Visibility flag ................................. 136\ Volume effects .................................. 151 **W**\ WAIT ....................................... 140,141\ WAV ............................................. 154\ WHILE ............................................ 25\ WRITE ........................................... 142 **X**\ XOR .............................................. 45