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アプリを制作した際の参考文献: C M Charles (1974) Teacher's petit Piaget (Belmont, Calif. : Fearon-Pitman) Piaget, Jean and R. Garcia. (1974) Understanding Causality. 박양덕 (2000) A comparison of teachers' recognition of the early childhood mathematics education with parents' 안애리 (1993) Degree of Cognition about written numerals used everyday environment Kamii C. (1985) Young Children Reinvent Arithmetic: Implications of Piaget's Theory. Lauren B Resnick, Susan F Omanson (1987) Learning to understand arithmetic.