R = (
    set(['A','B','D']),
    set(['B','C','E']),
    set(['D','E'])
)

F = (
    (set(['A']),set(['B','D'])),
    (set(['D']),set(['A'])),
    (set(['C']),set(['B','E'])),
    (set(['E']),set(['D'])),
    (set(['C']),set(['A']))
)

def closure(X, F):
    res = X
    mark = [0] * len(F)
    while 1:
        pre_visted = sum(mark)
        for i in range(len(F)):
            if mark[i] == 0: # not visited
                if F[i][0].issubset(res):
                    res = res.union(F[i][1])
                    mark[i] = 1
        after_visted = sum(mark)
        if pre_visted == after_visted:
            break
    return res

G = []
closures = tuple(
    (k, closure(k, F)) 
    for k, _ in F
) # (X, X+)
for idx, (X, Y) in enumerate(F):
    for rho in R:
        if X.issubset(rho):
            temp = closures[idx][1] & rho - X
            if len(temp) > 0:
                G.append((X, temp))
G

[({'A'}, {'B', 'D'}),
 ({'D'}, {'A', 'B'}),
 ({'C'}, {'B', 'E'}),
 ({'E'}, {'B'}),
 ({'E'}, {'D'}),
 ({'C'}, {'B', 'E'})]

The FDs in F are contained in G except for $C\rightarrow A$, and MEMBER $(G, C\rightarrow A)$ is true. Therefore, $\rho$ keeps dependency preservation.