invariant

Dehn showed that it’s possible to use the angles of any polyhedral shape — like a tetrahedron or a cube — to calculate a single quantity, now called the Dehn invariant.

Now the possibility of translation implies the existence of an invariant.

Thus, to decipher a cryptogram is to seek what in this document remains invariant, when the letters are permuted.

What now is the nature of this invariant it is easy to understand, and a word will suffice us.

Among words that have had the most fortunate influence I would select 'group' and 'invariant.'

Invariant virtue appears to be as mechanical as uninterrupted vice, for true excellence changes with conditions.