add checkmark for leanok command in print mode

[acmepjz]

... to align with web mode behavior. Personally I think it looks good.

[PatrickMassot]

I’m a bit worried that this would make the checkmark appear in a random place since people don’t expect this command to have some pdf output and its precise placement doesn’t matter to plasTeX. Do you have examples of well-known blueprints rendered with this modification?

[acmepjz]

Maybe you can see here https://acmepjz.github.io/lean-iwasawa/blueprint/sect0003.html#pseudo-null-criterion and the corresponding pdf file https://acmepjz.github.io/lean-iwasawa/blueprint.pdf (proposition 3.6, around page 5)

... this would make the checkmark appear in a random place since people don’t expect this command to have some pdf output and its precise placement doesn’t matter to plasTeX.

Yes you're right. In the web output, the checkmark always appeared in the beginning of the proposition. This would be also true for pdf if the \leanok command is in the beginning of proposition body (but not at the end, for example).