The document discusses a meetup about collaborative energy futures using blockchain and Ethereum in Madrid on October 20, 2016. It addresses the problem of double spending in transactions and how the Ethereum blockchain provides a transparent, resilient, and immutable record of transactions.

1. Meetup
Blockchain & Ethereum Madrid
20 de octubre 2016
Hacia un futuro de energía
colaborativo

2. IN CRYPTO WE TRUST

4. wallet
17BFVGTnJTmFBPVJZM1HRdNNWhXRb2HXjA
scan &
pay

5. El problema del ‘Double Spending’
ID - 255
2 0
ID - 256
2 0
ID - 255
2 0
ID - 256
2 0
ID - 257
2 1

6. Transaction
From: Tomás
(1a54gh8…)
To: Alicia (17erf0h2…)
Amount: 100
304532dv5fjj894n
apofh9a894hhfal...
TRANSACTION
POOL
BLOCK #41
BLOCK #40
BLOCK #39
BLOCK #38
BLOCK #37

7. TRANSACTION
POOL
BLOCK #42
BLOCK #41
BLOCK #40
BLOCK #39
BLOCK #38
BLOCK #37

8. Transaction
From: Tomás (1a54gh8…)
To: Alicia (17erf0h2…)
Amount: 5
304532dv5fjj894n
apofh9a894hhfal...

9. Transparente Resiliente Inmutable

11. ethereum