the simple thematic present tense. Two sets of endings are provided for the primary middle forms, as described above. The above assumptions about PIE phonology apply, in addition to a rule that deletes laryngeals which occur in the sequence -oRHC or -oRH#, where R stands for any resonant, H any laryngeal, C any consonant and # the end of a word. The most important effect of this rule is to delete most occurrences of in the thematic optative. Post-PIE developments The various verb formations came to be reorganised in the daughter languages. The tendency was for various forms to become integrated into a single "paradigm" which combined verbs of different aspects into a coherent whole. This process proceeded in steps: Combining different forms with similar meanings into a system of three major aspects. The result of this was the so-called "Cowgill–Rix" system described above, which was completed in late PIE, shortly after Tocharian had split off and well after the Anatolian split. At this stage, formations that originally had various purposes had their semantics largely harmonized into one of the aspect classes, with a clear distinction between primary and secondary derivations. These formations, however, were still separate lexical verbs, still sometimes with idiosyncratic meanings, and for a given aspect a root could still form multiple verbs or no verbs in that particular aspect. This is the stage visible in early Vedic Sanskrit. Combining the various aspects under a single unified verb, with a clear distinction between inflectional and derivational forms. This involved pruning multiple verbs formed from the same root with the same aspect, and creating new verbs for aspects that were missing for certain roots. At this stage a single verb was defined by a set of principal parts, each of which (approximately) defined the type of formation used in each of its aspects. This stage was in process in Vedic Sanskrit and was largely completed in Ancient Greek, although even in this language there are still verbs lacking some of the aspects, as well as occasional multiple formations for the same aspect, with distinct and idiosyncratic meanings. Many remnants of this stage are also found in Old Church Slavonic, which still had distinct stems for the present, aorist and infinitive/participle. Most Slavic languages later lost the aorist, but verbs still have distinct (and unpredictable) present and infinitive stems up to the present day. Regularizing the formations into "conjugations"