Perhaps you should try some spelling variations:
"Hilbert's test problem" » "Hilbert's text problem", "Hilbert's west problem", "Hilbert's best problem"
"Hilbert's tent problem" » "Hilbert's tenti problem", "Hilbert's text problem", "Hilbert's kent problem"
"Hilbert's texth problems" » "Hilbert's texto problems", "Hilbert's text problems", "Hilbert's texts problems", "Hilbert's texth problemas", "Hilbert's texth problema"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"Hilbert's test problem\") OR (\"Hilbert's tent problem\"))) OR (\"Hilbert's texth problems\"))~".
• Removing quotes may allow a broader search: (((( Hilbert's test problem ) OR ( Hilbert's tent problem ))) OR ( Hilbert's texth problems ))~.
• Adding a wildcard symbol may retrieve word variants: (((("Hilbert's test problem") OR ("Hilbert's tent problem"))) OR ("Hilbert's texth problems"))*.