Perhaps you should try some spelling variations:
"formal languages and estimation theory" » "formal languages and optimization theory", "formal language and estimation theory"
"formal languages and automation theory" » "formal languages and automata theory", "formal languages and animation theory", "formal languages and automated theory", "formal language and automation theory"
"formal languages and automatic theorem" » "formal languages and automated theorem", "formal languages and automata theory", "formal language and automatic theorem"

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