Simplify the following text for a Grade 8 native English-speaking person.
Original: Spencer-Brown 's philosophy was influenced by Ludwig Wittgenstein , R.D. Laing , Charles Sanders Peirce , Bertrand Russell , and Alfred North Whitehead .
Simplified: Spencer-Brown was influenced by Wittgenstein and R. D. Laing . LoF also echoes a number of themes from the writings of Charles Sanders Peirce , Bertrand Russell , and Alfred North Whitehead .