phantom and substitution only without result

[xyont]

hi, i do testing new feature of subtitution with double equal commands and results look great, many thanks.

however, it seems not working well if combined with phantom. Also, i'mi missing subtitution only without result to match display exactly as in textbook and report. This can be useful since many equation or formula in engineering have medium to long size of length, and a single line for both of them could umake nreadable clearly or may lost.