21. A computer system as recited in claim 20 wherein said editing means includes: means for detecting an edit made to an equation displayed upon said display screen having a valid parsed tree; means for determining whether said edit changes the structure of said parsed tree; and means for editing said parsed tree if said edit does not change the structure of said parsed tree.
21. A computer system as recited in claim 20 wherein said editing means includes: means for detecting an edit made to an equation displayed upon said display screen having a valid parsed tree; means for determining whether said edit changes the structure of said parsed tree; and means for editing said parsed tree if said edit does not change the structure of said parsed tree. 23. A computer system as recited in claim 21 wherein said parser is included in a recognition domain, and said computer system further comprises a plurality of recognition domains, each including a parser, said recognition domains including: a strokes recognition domain; a word recognition domain coupled to an output of said strokes recognition domain; a math symbols recognition domain coupled to an output of said word recognition domain; and a calculation recognition domain coupled to an output of said math symbols recognition domain.