Translate the given Spanish text to English

Material P comprises two or more cyclic carbonate groups (bi).
El material P comprende dos o mas grupos carbonatos ciclicos (bi).

Systems for showing such relationships are described.
Se describen sistemas para mostrar tales relaciones.

5,5'-diformyl-2,2'-difuran is prepared in excellent yield by photochemically irradiating furfural or a mixture of furfural and 5-bromo-2-furfural.

?-difurano, con excelentes rendimientos, por irradiar fotoquimicamente el furfural o una mezcla del furfural y un 5-bromo-2-furfural.

