PROCEDURE GET_NUM_SCR_ENTRIES ( direction : ExpandDirection );
   EXTERNAL;
PROCEDURE DEF_VERT_GRID;
   EXTERNAL;
PROCEDURE DEF_SHEET_AREA;
   EXTERNAL;
PROCEDURE DRAW_SHEET ( extent                              : ExtentType;
                       row_start,row_end,col_start,col_end : INTEGER;
                       blit_flag                           : BOOLEAN     );
   EXTERNAL;
PROCEDURE DATA_CLIP;
   EXTERNAL;
PROCEDURE TOGGLE_INVERSE ( color,row,col : INTEGER );
   EXTERNAL;
PROCEDURE DRAW_CELL ( row,col : INTEGER; force : BOOLEAN );
   EXTERNAL;
PROCEDURE DISPLAY_DATA ( extent                              : ExtentType;
                         row_begin,row_end,col_begin,col_end : INTEGER     );
   EXTERNAL;
PROCEDURE SET_UP_CELL_NAME;
   EXTERNAL;
PROCEDURE WRITE_CELL_NAME;
   EXTERNAL;
PROCEDURE SHEET_REDRAW ( extent    : ExtentType;
                         blit_flag : BOOLEAN;
                         direction : BlitDirection );
   EXTERNAL;