From the concluding paragraph of a new book by
mathematician Michael Harris:

"A team of eminent scholars is completing a definitive
edition of Hausdorff’s collected works—'unique …
in the annals of mathematical publishing'— with the
care befitting the literary figure he undoubtedly was….
… he is honored as, perhaps, the first modern
mathematician to give a name to what we have been
calling the 'relaxed field'— he called it the
'Spielraum  of thought'— and as a mathematician
who never lost his sensitivity to his chosen field’s
problematic attractions while remaining fully aware that
every veil lifted only reveals another veil."

— Harris, Michael, Mathematics without Apologies:
Portrait of a Problematic Vocation  (2015-01-18) 
(pp. 324-325). Princeton U. Press. Kindle Edition. 

Related material:  Spiel ist nicht Spielerei .