Perhaps you should try some spelling variations:
"nilpotent line groups" » "nilpotent lie groups", "nilpotent cone groups", "nilpotenti e groups", "nilpotent line group", "nilpotent linear groups"
"nilpotent link groups" » "nilpotent lie groups", "nilpotent cone groups", "nilpotent leibniz groups", "nilpotent linear groups", "nilpotent online groups", "nilpotent amino groups"
"nilpotent risk groups" » "nilpotent lie groups", "nilpotent orbits groups"

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• Performing a fuzzy search may retrieve terms with similar spellings: (("nilpotent line groups") or ((("nilpotent link groups") OR ("nilpotent risk groups"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("nilpotent line groups") OR ((("nilpotent link groups") OR ("nilpotent risk groups")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"nilpotent line groups\") or (((\"nilpotent link groups\") OR (\"nilpotent risk groups\"))))".
• Removing quotes may allow a broader search: (( nilpotent line groups ) or ((( nilpotent link groups ) OR ( nilpotent risk groups )))).
• Adding a wildcard symbol may retrieve word variants: (("nilpotent line groups") or ((("nilpotent link groups") OR ("nilpotent risk groups"))))*.