Perhaps you should try some spelling variations:
"block space" » "block spaces", "bloch space", "block sparse"
"blank space" » "blank spaces", "blank slate", "blank slates"
"black space" » "black spruce", "blank spaces", "black race"
"slack space" » "stack space"

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("block space") OR ("slack space"))) OR ((("blank space") OR ("black space")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"block space\") or (\"slack space\"))) or (((\"blank space\") OR (\"black space\"))))".
• Removing quotes may allow a broader search: (((( block space ) or ( slack space ))) or ((( blank space ) OR ( black space )))).
• Adding a wildcard symbol may retrieve word variants: (((("block space") or ("slack space"))) or ((("blank space") OR ("black space"))))*.