[...] ‘variants’ are correlates with mutual substitution.
- Hjelmslev (1961), a pag.74

[...] not only entities, but also functions have variants, so that the distinction between variants and invariants is valid for functives in general.
- Hjelmslev (1961), a pag.62

In the modern phonetically oriented science of the expression it is the custom to distinguish between two kinds of variants – the so-called “free” variants, which appear independently of the environments, and the so-called “bound” or “conditioned” [...] variants, which appear only in certain environments in the chain.
- Hjelmslev (1961), a pag.81-82