Displaying text in facsmile

Despite an abundance of text editors for microcomputers, it is difficult to edit texts of a mathematical nature an small systems. Some editors are only capable of a rudimentary notation, and almost all make editing difficult because the text shown on the screen often bears little resemblance to the text that will eventually be printed. Editing text in facsimile lets the user work with the meaning and format of a text without being distracted by special symbols, key words, and formatting information. The editor interprets this information for the current logical screen as it would during the printing process, and is able to display this facsimile on the physical video screen. The physical video screen can be described by a type scheme in the sense of a concrete computational structure from an abstract data type. In particular, character patterns can be displayed at any pixel location. The type scheme was implemented in PASCAL/MT+ for a low-resolution, bit-mapped video terminal with a Z80A-based microcomputer.