20 Years !

My friend Ada was slowly recovering from a heart attack.
"Doctor," she pleaded with her cardiologist, "you must keep me alive for the next two years. I want to attend my first grandchild's bar mitzvah."
"We'll try," he replied compassionately.
In due course Ada gratefully attended the festive rite of passage.
Some time later she again spoke to her doctor. "My granddaughter is to be married in 18 months. Please help me to be able to attend her wedding."
"We'll do our best," he replied.
And my friend happily attended her granddaughter's wedding.
Ten years passed. Ada visited her cardiologist regularly and followed his instructions religiously. One morning she called him. "Doctor," she began, "I'm feeling fine, but I have another request to ask of you:
Remember how you saw me through to my grandson's bar mitzvah?"
"Yes."
"And later how you helped me attend my granddaughter's wedding?"
"Yes."
"Well, as you know I've just celebrated my 80th birthday. And I just bought myself a new mattress."
"Yes?"
"It has a 20-year guarantee..."