Implemented SLOT-VALUE and (partially) SLOT-MISSING.
Implemented SLOT-VALUE and (partially) SLOT-MISSING.

clasp-developers/SICL,clasp-developers/SICL,vtomole/SICL,vtomole/SICL,clasp-developers/SICL,clasp-developers/SICL,vtomole/SICL,vtomole/SICL